A five-minute scan could be used to spot people at risk of dementia before symptoms appear, researchers claim.

Scientists used ultrasound scanners to look at blood vessels in the necks of more than 3,000 people and monitored them over the next 15 years.

They found those with the most intense pulses went on to experience greater cognitive decline over the next decade than the other study participants.

Researchers hope it may offer a new way to predict cognitive decline.

An international team of experts, led by University College London (UCL), measured the intensity of the pulse travelling towards the brain in 3,191 people in 2002.

A more intense pulse can cause damage to the small vessels of the brain, structural changes in the brain's blood vessel network and minor bleeds known as mini-strokes.

Over the next 15 years, researchers monitored participants' memory and problem-solving ability.

Those with the highest intensity pulse (the top quarter of participants) at the beginning of the study were about 50% more likely to show accelerated cognitive decline over the next decade compared with the rest of the participants, the study found.

Researchers said this was the equivalent of about an extra one to one-and-half years of decline.

Cognitive decline is often one of the first signs of dementia, but not everyone who experiences it will go on to develop the condition.

Researchers said the test could provide a new way to identify people who are at risk of developing dementia, leading to earlier treatments and lifestyle interventions.

Controlling blood pressure and cholesterol, having a healthy diet, doing regular exercise and not smoking can all help to stave off dementia, evidence suggests.

Dr Scott Chiesa, from UCL, said: "Dementia is the end result of decades of damage, so by the time people get dementia it's too late to do anything.

"What we're trying to say is you need to get in as early as possible, identify a way to see who's actually progressing towards possibly getting dementia and target them."

However, the study, co-funded by the British Heart Foundation, does not contain data on which study participants went on to develop dementia.

Researchers next plan to use MRI scans to check if people in the study also display structural and functional changes within the brain that may explain their cognitive decline.

They also want to test whether the scan improves predictive risk scores for dementia which already exist.

Dr Carol Routledge, director of research at Alzheimer's Research UK, said it was not yet clear if the scan could improve the diagnosis of dementia.

She added: "What we do know is that the blood supply in the brain is incredibly important, and that maintaining a healthy heart and blood pressure is associated with a lower risk of developing dementia."